This invention relates to a novel, low temperature process for obtaining high yields of products using a catalytic hydride reduction method. Sodium hydride is a strong reducing agent, capable thermodynamically of entering into many hydride transfer reactions of the type: EQU NaH+MX.fwdarw.MH+NaX, (1)
where M is a metal, metalloid or metalloid-containing radical, and X is an electronegative group; such as a halogen, alkoxy radical, etc.
However, in practice many such reactions take place too slowly to be useful. For example, it is well known in the art that sodium hydride fails to reduce chlorosilanes (for example, wherein M=(CH.sub.3).sub.3 Si, and X=Cl) at room temperature in the absence of catalysts. Since sodium hydride is the least expensive alkali metal hydride and is readily available commercially in large quantities, several investigations have been devoted to finding conditions under which its reduction potential could be utilized practically.
Using high temperatures (about 250 C), Cooper and Gilbert (U.S. Pat. No. 3,099,672) were able to successfully reduce chlorosilanes with sodium hydride at a practical rate, and with high conversion. However, this approach is restricted to cases in which both the reactants and products are stable at these high temperatures. Milder conditions were achieved by Chalk (U.S. Pat. No. 3,535,092), who discovered special catalytic solvents, such as hexamethylphosphoramide, in which chlorosilane reduction could be carried out at room temperature. However, this solvent is expensive, and also is a suspected carcinogen. Jenkner (U.S. Pat. No. 3,043,857) disclosed alkyl compounds of boron, aluminum and gallium which also catalyze reductions with sodium hydride. These catalysts have the disadvantage that they react violently with water, and are spontaneously flammable in air. Since both sodium hydride and the reduction products are flammable, the use of spontaneously flammable catalysts poses a severe fire hazard. Jenkner also mentions the non-pyrophoric alkoxy-and phenoxy-compounds of boron and aluminum as catalysts, but they are much less active than the pyrophoric alkyls, and require high temperatures (e.g., 150 C) and high concentrations to be effective. U.S. Pat. No. 3,496,206 discloses a somewhat similar process providing however, a less volatile catalyst form.